When a web material is continuously fed from a plurality of successive rolls, the ends of the rolls may be spliced together to eliminate interruption to the web feed. Different types of splices can be formed, including a lap splice, a butt splice, and a gap splice. A lap splice is formed when a portion of an expiring web overlies a portion of a web from a new roll with the under surface of the overlapped portion of one of the webs adhering to the upper surface of the other web. With a butt splice, the trailing end of the expiring web is in intimate contact with the leading end of the new web, but no overlap exists. A gap splice is formed when no overlap exists and the ends of the expiring web and new web are separated. For the butt splice and the gap splice, tape may be employed to connect the ends. U.S. Pat. No. 5,277,731 relates to the formation of a butt splice. U.S. Pat. No. 4,652,329 and U.S. Pat. No. 5,045,134 teach apparatus and methods for forming a splice.
The location of the splice may need to be detected if further processing of the web material is to be conducted. For example, if the web material is photographic paper, the location of the splice needs to be detected so that a printer does not record a photographic image on the portion of the photographic paper containing the splice. In the manufacturing process, the location/presence of a splice needs to be detected before cutting and slitting operations can occur.
Mechanical sensors or other contact devices may be employed. One method used to detect a splice is to mechanically monitor the difference in thickness of the web, signifying the passage of a splice. U.S. Pat. No. 3,854,643 relates to an apparatus for detecting a splice wherein an increased thickness of a splice imparts a slight movement in a pressure roller to indicate the presence of a splice. U.S. Pat. No. 4,314,757 relates to a splice detector for photographic paper wherein a splice warning slot in the paper activates a switch. U.S. Pat. No. 4,194,659 provides an example of an electromechanical seam detector for the textile industry. While such apparatus may be suited for their intended purpose, such mechanical and contact sensors require a lengthy set-up procedure, do not provide for variations in web thickness, are not suitable for fast moving webs, may induce scratches on the web, or generate static.
Optical sensors may be employed. However, such optical sensors are unsuitable for photosensitive web material. Ultrasonics have also been employed, but typically involved complicated circuitry and set-up procedures. U.S. Pat. No. 4,901,577 provides an example of an apparatus for detecting a splice using ultrasonics.
Accordingly, there exists a need for an apparatus and method for detecting a splice in a running length of web material. Such an apparatus and method should have a quick set-up procedure, operate for webs traveling at a high rate of speed, provide for variations in web thickness, not induce scratches in the web material, not generate static, and be suitable for photosensitive web material.